1. Field of the Invention
This invention broadly relates to a portable, lever operated mechanism for controlling the movement of an electric drill toward and away from a workpiece. More particularly, the present invention concerns an electric drill control mechanism having spaced apart mirror-image lever and linkage assemblies which each include a first lever pivotally coupled to a support carrying the drill, and a second lever pivotally connected to the first lever in such a fashion that swinging movement of a handle on the second lever causes the first lever to swing in an opposite direction and advance the support and the drill carried thereon toward the workpiece. The dual lever and linkage assemblies provide precise control over leveraged movement of the drill toward the workpiece while retaining the bit in an exact, perpendicular orientation relative to the surface of the workpiece as the drill is advanced or retracted along the full stroke length of the bit. The control mechanism is useful in such diverse applications as drilling into safes, installing anchors on walls for signs or constructing furniture.
2. Description of the Prior Art
Small, portable electric drills are used in a variety of applications and are especially convenient in circumstances where the workpiece is too large, heavy or bulky to be placed upon the table of a stationary, conventional drill press. However, it is difficult to hold the drill by hand in such an orientation that the longitudinal axis of the drill bit is held in a fixed position and exactly 90.degree. from the plane of the work surface. When drilling relatively hard materials, the operator is often unable to apply for extended periods of time a steady force as may be necessary for advancement of the bit.
As an example, large signs which are secured to vertical walls of buildings are often held in place by means of expandable anchors or other devices that are received within holes drilled in the wall. Unfortunately, the drill may unintentionally wobble slightly from side to side such that the resulting hole includes non-cylindrical, flared portions and may be somewhat larger than is desirable for securely retaining the anchor in place. However, once the holes are drilled in the wall, little can be done to correct the problem without undertaking substantial, additional steps.
Moreover, signs or other items which are supported by two or more wall anchors are often not provided with adjustment devices for accommodating variations in distance between the installed anchors. As a result, if one of the holes or bores for the anchors is drilled in such a fashion that the longitudinal or central axis of the bore is disposed at an angle other than a true, 90.degree. orientation from the plane of the wall surface, then lag screws or other devices which are typically received in the anchors project outwardly from the wall at an inclination which may correspondingly change the distance between adjacent lag screws from the intended dimension to such an extent that installation of the sign may be rendered difficult, if not impossible. In addition, the worker may be standing on a ladder, scaffold or other type of elevated platform in such a position that it is difficult to accurately assess the precise orientation of the drill bit relative to the wall.
As another example, it is desirable for locksmiths when drilling into safes to maintain the drill at all times at an exact, perpendicular orientation relative to the wall of the safe. These types of drilling operations are often only accomplished after a period of several hours due to the nature of the hardened material typically used in the fabrication of safes even though the wall of the safe may have a thickness of only one to two inches. As a consequence, maintenance of the drill bit at a precise, perpendicular orientation relative to the wall of the safe ensures that only a minimum of the hardened material need be removed by the bit.
More importantly, however, is the need for locksmiths to have precise control over advancement of the bit while being able to perceive or feel the speed of advancement of the drill bit when the latter reaches, for example, relatively soft materials. In many safes, the walls are comprised of an outer wall section of hardened steel and an inner, somewhat thinner wall section comprised of relatively softer steel. During the work operation, a hole is typically drilled directly over the lock mechanism so that tools may be inserted to manipulate and open the lock mechanism without destruction of the same. As a consequence, it is highly important that the user during advancement of the bit through the wall sections be able to perceive the relative ease of advancement of the bit when the latter reaches the softer, inner wall section so that the speed of advancement may be sufficiently reduced to avoid contact of the bit with the lock mechanism.
During the drilling of safes, excessive amounts of pressure need not be applied to the drill inasmuch as the drill may prematurely wear. However, steady amounts of pressure should be continuously applied to the drill in order to avoid undue lengthening of the period of time needed to complete the work operation. However, for the aforementioned reasons, the operator should at all times have a precise feeling for the rate of progression of the drill bit in order to instantly reduce pressure applied to the drill when necessary. As can be appreciated, it is sometimes difficult to accurately predict the respective thicknesses of the outer and inner wall sections of safes unless, of course, the locksmith has previously become intimately familiar with the perpendicular model and style of the safe being drilled.
In the past, it has been proposed to provide a lever or linkage arrangement in a relatively large, stationary drill press for shifting of a drill toward and away from a workpiece, in comparison to the rack and pinion mechanisms normally found on stationary drill presses. My attention has been called to the following patents: U.S. Pat. Nos. 1,272,108, 1,493,142, 1,852,736, 1,927,006, 2,038,422, 3,195,375 and 3,447,454. The lever mechanisms described and illustrated in these patents are not, however, dynamically arranged and balanced in such a fashion that the lever mechanisms may be used on significantly smaller, portable, hand-held rigs.
Certain of the aforementioned U.S. Patents, and in particular U.S. Pat. No. 3,447,454, describe lever and linkage assemblies which increase the mechanical advantage as a lower lever having a foot pedal is depressed to shift the drill downwardly into a workpiece. However, the two levers are interconnected by a link which is pivotally coupled to the second lever at a location that causes a reduction in a portion of the mechanical advantage gained by use of the first lever. While the lever arrangement depicted in U.S. Pat. No. 3,447,454 may be satisfactory for increasing the force generated by the user sufficiently to longitudinally shift the drill bit into relatively dense materials, the particular arrangement and position of the link interconnecting the two layers undesirably decreases the control and feel over the drilling operation.
My attention has been also called to two other U.S. Patents, namely U.S. Pat. Nos. 2,720,125, 4,442,905 and 4,582,456 wherein are described drill rigs having handle levers that swing in directions generally opposite to the direction of advancement of the drill bit into a workpiece. Again, the lever mechanisms of these rigs cannot be satisfactorily adapted for use with small, portable hand held drill control mechanisms.